The invention relates to a semiconductor device and a method for manufacturing the same.
In order to raise the speed of a transistor, studies and research have been extensively performed regarding a gate structure using a metal gate and a high-k gate insulating material to realize a low gate work function and a vertical electric field.
Generally, hafnium (Hf)-based metal gate oxide is used as the high-k gate insulating material. In this case, Hf pinning may occur on an interfacial surface between a gate electrode and the metal gate oxide or an interfacial surface between the metal gate oxide and a silicon substrate, thereby causing a flat band shift phenomenon.
Accordingly, a threshold voltage (Vth) of the transistor may be shifted, and degradation of negative bias temperature instability (NBTI) may be caused.